astronomy

Ice planet

Ice planet is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Ice planet rather than just read about it. In short: An ice planet or icy planet is a type of planet with an icy surface of volatiles such as water, ammonia, and methane. Ice planets consist of a global cryosphere.

Key takeaways

Ice planet belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Ice planet to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ice planet from memory before moving on to harder problems.

Reference excerpt

An ice planet or icy planet is a type of planet with an icy surface of volatiles such as water, ammonia, and methane. Ice planets consist of a global cryosphere. Under a geophysical definition of planet, the small icy worlds of the Solar System qualify as icy planets. These include most of the planetary-mass moons, such as Ganymede, Titan, Europa, Enceladus, and Triton; dwarf planets Pluto, Orcus, Haumea, Makemake, Quaoar, Sedna, Gonggong, and Eris; and the largest comets. In June 2020, NASA scientists reported that it is likely that exoplanets with oceans, including some with oceans that may lie beneath a layer of surface ice, may be common in the Milky Way galaxy, based on mathematical modeling studies. OGLE-2005-BLG-390Lb, first observed in 2005, is a possible ice planet.

Characteristics and habitability

An ice planet's surface can be composed of water, methane, ammonia, carbon dioxide (known as "dry ice"), carbon monoxide, nitrogen, and other volatiles, depending on its surface temperature. Ice planets would have surface temperatures below 260 K (−13 °C) if composed primarily of water, below 180 K (−93 °C) if primarily composed of CO2 and ammonia, and below 80 K (−193 °C) if composed primarily of methane. On the surface, ice planets are hostile to life forms like those living on Earth because they are extremely cold. Many ice worlds likely have subsurface oceans, warmed by internal heat or tidal forces from another nearby body. Liquid subsurface water would provide habitable conditions for life, including fish, plankton, and microorganisms. Subsurface plants as we know them could not exist because there is no sunlight to use for photosynthesis. Microorganisms can produce nutrients using specific chemicals (chemosynthesis) that may provide food and energy for other organisms. Some planets, if conditions are right, may have significant atmospheres and surface liquids like Saturn's moon Titan, which could be habitable for exotic forms of life.

Examples

In solar system Although there are many icy objects in the Solar System, none of them qualify as planets under the IAU definition of planet. However, most planetary-mass moons are ice-rock (e.g. Ganymede, Callisto, Enceladus, Titan, and Triton) or even primarily ice (e.g. Mimas, Tethys, Rhea, and Iapetus) and so qualify as ice planets under geophysical definitions of the term. The largest Kuiper belt objects, such as Pluto, Haumea, Makemake, Charon, Quaoar, and Orcus also qualify as such under geophysical definitions. Europa is also often considered an ice planet due to its surface ice, though its high density indicates that its interior is mostly rocky. The same is true for the scattered-disc object Eris.

Beyond solar system Dozens of known exoplanets are very probably ice planets, given their orbits, surfaces, densities, and host stars. Examples of ice planets include Gliese 667 C d, Gliese 667 C g, Kepler-441b, OGLE-2005-BLG-390Lb, OGLE-2013-BLG-0341LBb, OGLE-2016-BLG-1195Lb and MOA-2007-BLG-192Lb

See also Ice giant Icy moon Ocean world Snowball Earth Hoth – Fictional planet in Star Wars

References

Illustrations

Worked examples

Example 1 — a first encounter with Ice planet

Start with the simplest possible case. Write down what Ice planet claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Ice planet before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Ice planet ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Ice planet

In research: Ice planet appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Ice planet in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Ice planet is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ice, Terrestrial planets, Types of planet, so understanding it makes those chapters shorter.
In everyday life: Look for Ice planet outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Ice planet in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ice planet means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Ice planet out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ice planet in simple terms?

An ice planet or icy planet is a type of planet with an icy surface of volatiles such as water, ammonia, and methane. Ice planets consist of a global cryosphere.

Why does Ice planet matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Ice planet?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Ice planet.